Home » Paleontology
Category Archives: Paleontology
I was reading a post by Brian Switek on his blog Laelops—which by the way, if you aren’t reading it, you should—about interpreting injuries on dinosaur bones. It’s an interesting read, but what caught my eye was a problem that I have seen in more places than I can count. He included this picture in his post. Take at look at the front limbs.
The “hands” are pointed inwards. To get in this position, the elbows have to be turned outwards, using a rotation in the shoulders. But it also requires the hands to be pronated. To get what I mean by that, hold your hands forward with the palms up. When you do this, the two bones in your forearms—the ulna and the radius—are positioned side by side.
This position is called supination. Pronation requires the radius to rotate so that it crosses over the ulna. This can be done because of the construction of the elbow. The ulna is essentially the entire elbow joint, making it a hinge type joint. The radius is, for the most part, just along for the ride at the elbow. The head—the part at the elbow—is round, with a shallow indentation, which is surrounded by what is called the annular ligament. That ligament wraps around the radius, attaching it to the ulna, but never actually attaching to the radius itself, allowing the head to spin in the sling. It is that shape of the radius and the annular ligament that allows it to rotate freely, which makes our level of pronation possible.
Importantly, all tetrapods have the same bones. It was set in place from the first fish that developed bones to support their fins and remains that way all through the hundreds of millions of years to us today. However, not all animals have the same shape of the radial head. Some animals appear to not have both bones, but in reality, they do. They have just fused the bones together. But that fusion has consequences, just like altering the shape of the radial head.
Before we move on to dinosaurs and those consequences, it would be reasonable to ask about other animals to see if they show the same pattern. Let’s take a look at proboscideans, the family of elephants. They are large animals that have their palms facing downward.
This is an elephant skeleton on display at the Manchester Museum. They have a radius and ulna, just like humans. Theirs, however, do not swivel. Nevertheless, it is rotated so that the bones are not in parallel, but the two ends are twisted so that the radius is twisted over the ulna. Their forelimbs are in permanent pronation.
So what about dinosaurs? Let’s look at Dreadnaughtus, the giant sauropod.
This is Figure 2 from Lacovara et al. 2014. The radius and ulna are massive, as befits a giant quadruped. They are also incapable of rotating to pronate the foot. It has been said by some that some degree of pronation is required for efficient quadrupedal locomotion, but that is not really accurate. It does mean though, that the first digit, what would be our thumb, is going to face forward or at most slightly inward while the remaining digits will be angled outward (anterolaterally). They will not be situated directly forward without shifting the arms at the shoulder. As an example, here is a figure showing a sauropod trackway. Note the direction of the toes.
This is a figure from Falkingham, et al. 2010. As can be seen, the toes are not forward, but pointing outward. The level of pronation is minor and can be achieved with only rotation at the shoulder and a minimal shift or the forelimb. VanBuren and Bonnan (2013) found this was true in all quadrupedal dinosaurs.
This is a best case for pronation in dinosaurs and they can’t do the full pronation needed for bunny hands, much less the bizarre inward facing hands of the Plateosaurus above. So let’s look at theropods, where we see bunny hands all the time. For instance, in Jurassic Park pretty much all the dinosaurs have bunny hands.
The palms are downward with the arms close in, requiring a full pronation to achieve that position. So could they do it? To the bones. This is the radius of Neuquenraptor, as published by Novas and Pol in 2005. It is an unenlagiin, in the family Dromaeosauridae, along with Velociraptor, Deinonychus, and all those other raptor dinosaurs.
These radius is fairly straight, and if you look at the head, it is not the shallowly indented round cup we see in mammals. It is more angular, which is typical of theropods. That relative angularity would prevent the radius from rotating as ours do, in effect locking it into a small range of motion, preventing them from placing their hands palm down.
In point of fact, VanBuren and Bonnan didn’t just look at sauropods. They looked at all types of dinosaurs. They found that no dinosaur had the ability to cross the radius over the ulna, which means that at best, they had very limited ability to pronate their forearms. That means no known dinosaur could have characteristically held their arms close in with their palms facing downward, aka bunny hands.
It is a little more complicated than this. Studies have shown that if the arm is fully extended, the hands can be more pronated, by using the entire length of the arm to rotate, but even that is not going to be fully pronated like we can, or bunnies can. And if you think about the living dinosaurs, the birds, when was the last time you saw a bird put its wings flat on the ground in front of them? They can clap, but they can’t type or play basketball.
Of course, the wrist bones of the maniraptors—those dinosaurs leading up to birds—did have what is called a semilunate carpal bone, allowing them to move their hands to insane degrees side to side, which is what allowed them to develop the ability to fold their wings like they do, and they can flex and extend their hands to a remarkable degree. But they cannot rotate their wrist. Try it yourself. See what movements you can make with your hand without moving your forearm, just your hand. However far you can move your hand that way, these dinosaurs have you beat in spades. But once you move that forearm, you have a serious advantage over them.
Back in the old days, before the idea of museums being educational centers became commonplace, most museums were more like some rich person’s trinkets collected during vacations packed into glass cases so people could see them. They rarely had signs telling people what anything was, nor was there oftentimes any attempt at organization. Because of the rather haphazard and all-encompassing nature of the displays, they got the name Cabinets of Curiosities.
As time went on, they became more thoughtful and organized, with more attention being spent on telling people what the objects were, teaching people about them, and properly preserving the objects for posterity.
The Old State House Museum in Little Rock honors that tradition with an exhibit called “Cabinets of Curiosities: Treasure of the University of Arkansas Museum Collection.” I am sad to say that the exhibit has been up since March 11 of 2017, but I have only recently learned about it and have gone to see it. Truth be told, the only reason I found out about it was because I went to the University of Arkansas at Fayetteville to see the Hazen Mammoth fossils and found that the lower jaw of that mammoth was on display in Little Rock.
The reason I am sad to say this is because the exhibit is well worth your time to go see. If I had known about it earlier, I would definitely have discussed it here by now. I was told it will still be at the museum for another year, so you still have time. It is free, so go. Spend a Saturday downtown and explore the exhibit. Then go see what else is down there, which is plenty to keep you busy over the weekend.
What will you see when you are there? To begin with, you might want to ask directions from their helpful and friendly staff, because the exhibit is upstairs in a side gallery that you might miss if you didn’t know it was there.
The objects are from the University of Arkansas Museum at Fayetteville, which, sadly, closed its doors in 2003. As a result, if you want to see their collections, you have to make an appointment to see the warehoused collections. Or you can see a small part of them in this exhibit. The museum had collections from all over the world covering many subjects, which the exhibit honors by having selections of a wide range. It is like a mini-museum of anthropology and natural history.
I am a fossil guy, so I am going to focus on the fossils you can see. The fossils are mostly in the first two rooms that you enter in the exhibit. In the first room, under the horns of a large cervid (the family containing deer, elk, and moose), are two cabinets of invertebrate fossils and minerals. There are some nice fossils to see. You can see a crinoid with the calyx, or body, and pinnules, or “fronds”. These are much rarer than the pieces of stalks we normally find throughout the Ozarks. There is also a starfish, ammonoids, and nice plant fossils, among others.
To the right of this display is a cabinet containing the skulls of a musk ox and Smilodon (saber-toothed tiger), a couple of large, straight-shelled nautiloids, and one of the bones of Arkansaurus, which up until very recently, was the only known dinosaur found in Arkansas.
On the other side of the room, you can see the bones of an elephant leg and a cabinet full of geology specimens, including one enormous quartz crystal that would not be allowed as a carry-on for some planes because it is too big to fit.
The next room contains case with the leg bones of a camel, lion, dog, and cat. It also contains the pieces of mammoth that I came to see. But before you get to that case, you have to pass a giant clam that could fit a child, or even a small adult if they curled up.
The other side of the room contains the skulls of a bison and rhino, a whale rib, and an entire icthyosaur from Germany. The end of the room has the skulls of a bear and walrus, complete with tusks, and the skeletons of a bat and snake.
The final part of the fossil and biology section that I was most interested in was an old display of horse evolution. If made today, it would probably look substantially different because of all the new data we have gotten since that display was made; but except for a few very minor details, the essential facts would be the same.
Of course, there is much more to the exhibit than what I have presented here, such as this cool whalebone armor and cavalry sword, so spend some time checking out the rest of the exhibit and the museum.
There is one thing that the exhibit could have capitalized on, but didn’t (mainly because they didn’t know about it, but also because they were trying to stay with the whole cabinets of curiosity motif), was that many of the fossils and biology specimens have fossil counterparts that have been found in Arkansas. For instance, we have fossil Smilodons, musk oxen, whales, several mastodons, giant deer and giant snakes, and much more.
So here is my question to you. How many people would pay for a special tour of the exhibit that discussed all the cool Arkansas fossils that matched up with the ones on display here. How much would you pay? $10/person? More? Less?
On March 12-13, the south-central section of the Geological Society of America held their annual meeting in Little Rock, Arkansas. During that meeting, a session was held on paleontology in honor of Arkansaurus fridayi being named our State Dinosaur, even though it has never been officially scientifically named and it being the only dinosaur that has ever been found in Arkansas other than tracks. That all changed during the meeting. This post will focus on the Arkansas dinosaurs (yes, plural, that was not a typo). A later post will cover more fossil announcements.
The first talk on Arkansas dinosaurs came from our very own Dr. Rebecca Hunt-Foster, who did the initial work on Arkansaurus. She has a new paper that came out right after the meeting. She announced that Arkansaurus fridayi is now the officially recognized scientific name for our dinosaur. She also discussed her findings confirming it as an ornithomimid, one of the bird-mimics, like the Gallimimus made famous in Jurassic Park. That had been the first tentative identification, but her work previously showed that it did not match with other known North American ornithomimids. However, that was from a total known collection of nine specimens. We now have almost two dozen ornithomimids known from North America. When she compared Arkansaurus with the new material, she was able to confirm that the initial identification was indeed correct. Moreover, it showed that ornithomimids had the ability to disperse across the continent at the time. The Late Cretaceous interior seaway that bisected the continent had not yet closed off access by then.
Dr. Celina Suarez from the University of Arkansas at Fayetteville provided the most astounding talk of the session (ed. this was a repeat of the talk she gave at the national GSA meeting in Seattle in 2017). We knew we had titanosaurs and acrocanthosaurs in Arkansas from their foot prints. Now we have their bones as well. She presented a description of the first known Mesozoic multi-faunal vertebrate assemblage in Arkansas. In other words, she reported a collection of fossils that contained several different species. The fossils were found in Howard County within the Holly Creek Formation, a part of the Trinity Group that underlies the DeQueen Limestone. This is the same site which became famous for its dinosaur tracks.
Among the fossils included pieces of a titanosaur that is probably Sauroposeidon, one of the largest dinosaurs ever known. They like to call it Paluxysaurus in Texas, but further work has indicated that Paluxysaurus is a junior synonym of Sauroposeidon found in Oklahoma and now Arkansas. She also found pieces of an Acrocanthosaurus. For those who are not familiar with this dinosaur, it is a carcharodontosaurid, the same family as Giganotosaurus. This family is within Allosauroidea, the group containing Allosaurus and all its kin. Acrocanthosaurus was almost the size of Tyrannosaurus rex and with a small sail or ridge along its back and was the dominant predator of its time.
That isn’t all though. They also found scutes from an ankylosaur. While it isn’t a lot, Kristy Morgan, one of her students, was able to determine that they likely belonged to a nodosaurid ankylosaur either most closely related to or actually was Borealopelta, a dinosaur from Canada just named in 2017 from the best preserved dinosaur fossil ever found.
Finally, pieces of two other theropods were found. They found pieces identified as Deinonychus antirropus, Velociraptor’s big cousin, as well as Richardoestia. Deinonychus is well known as the archetypal dromeosaur, the dinosaurs with the famed sickle-clawed toe. Richardoestia is much less well known, making this identification curious. All that is really known of this dinosaur is a set of jaws and some isolated teeth. Three species have been named, but at least one has been suggested to be a sebecid crocodylomorph. It is likely that once more of this genus is discovered, some or all of the species will not survive, at least as they are now. But for now, we will count it as an Arkansas dinosaur until shown otherwise.
This just touches on the fossils found in this assemblage. We now have a much bigger glimpse into Cretaceous Arkansas. Stay tuned for more. For now, we can say that southwest Arkansas 120 million years ago looked something like this.
Three years ago, a ten year old boy was visiting a monastery in Colombia. Being a curious boy, he looked around at his surroundings. He could have done like others have done for centuries and not paid that much attention to the stones upon which he walked, but he didn’t. He noticed a curious fossil fish in one of the flagstones. Most people, if they noticed it at all, would have simply given it a passing nod of interest. He, on the other hand, took a picture of it and sent it to the local Paleontology Research Center to see if they knew what it was.
Firstly, I amazed they even had a local paleontology research center, most places don’t. Secondly, it is amazing that the boy took the time to bring it to their attention. Thirdly, it is amazing that someone there noticed what they had and brought it to the attention of the needed experts. All these amazing, unusual occurrences have resulted in an article in the January 31 edition of the Journal of Systematic Paleontology detailing the new fossil species discovered by that boy. Sadly, no one knows how to contact him to let him know about the publication. The researchers have his name and email, but have apparently been unable to contact him to give him his copy of the paper about his fish.
The fish he discovered was named Candelarhynchus padillai, after the Monastery of LaCandelaria near Ráquira, Colombia, where it was found. The stone for the flagstone came from a nearby quarry. According to the authors of the paper, the rocks in the quarry corresponding to the flagstones were “fossiliferous, finely laminated, light to dark grey, indurated mudstones ofthe lower-middle Tuonian San Rafael Formation…” The rock strata also contained numerous plankton, ammonites, clams, and crabs; so quite a rich fauna. The Turonian is 89.8-93.9 Mya, according to the latest GSA time scale, so we are talking roughly 92 Mya.
The fossil is excellently preserved, with slabs containing both part and counterpart, meaning that when they split the slab, pieces and impressions were left on both sides. The whole body can be seen, with nice detail around the head, as well as impressions of the soft tissue portions of the fins. At 27 cm (just over one foot), it is a decent-sized fish. It’s a thin fish, with a long skull full of tiny, conical teeth. It was clearly a fast-swimming predator, and likely prey for a lot of larger species.
The reports on the fish said that it does not have any living relatives. That is true, in a way, but also not. The specific family the phylogenetic analysis placed it in is Dercetidae, an extinct family that all died out in the Cretaceous. However, if we look a bit broader, it is in the Order Aulopiformes. This order is mostly known for a variety of mostly deep water fish known as lizard fishes, which is why all the news reports of this find have said Candelarynchus was a “lizard fish.” Even though it is in the same Order, it is not in the same family as any of the modern lizard fish.
But the title of this post mentioned Arkansas and I have thus far not done so. Vernygora reports that current analyses of fossil aulopiforms include three main families: the Dercetidae, Halecidae, and the Enchodontidae. One of the most prominent Cretaceous fish from Arkansas is Enchodus, commonly called the “saber-toothed herring.”
This is a terrible name because Enchodus has nothing to do with herrings. It was at one time considered part of Salmoniformes, making it closer to salmon. However, more recent analyses have consistently placed it in Aulopiformes, specifically within the Enchodontidae, making it closer to lizard fish. This makes a good deal of sense to me because, if you add the fangs from a payara, commonly known as the vampire fish, onto a lizard fish, you have pretty good idea of what Enchodus was like.
Fossil lizard fish then were quite abundant in the Late Cretaceous in both worldwide range and diversity. They may not be the most recognized fish today, but they have a long history and make for great fossils that can be found in a lot of places, including southwestern Arkansas.
Did you know that Arkansas once had catfish more than three meters long and weighing, depending on who you believe, as much as 450 kg? That makes the world record catfish of today look positively puny.
The proof can be found at the Arkansas Geological Survey. The skull of one such monster is on display in the second floor display case. It was found in 1983 off Highway 79 near Camden. The bones were pulled from the Claiborne Formation, or more specifically, the Sparta Sand.
The Claiborne Group can be found in much of the South-Central part of the state, as well as on Crowley’s Ridge. It is Eocene in age (34-56 Mya). According to the Arkansas Geological Survey, the Claiborne is primarily non-marine and is comprised of mostly fine-grained rocks ranging from silty clays to medium-grained sandstones, with the occasional lignitic coal bed. The shales usually have the variegated tans and grays often seen in terrestrial sediments, with brown and black organic-enriched layers intermixed. Fossils are common from the units, with plant fossils common, as well as trace fossils. Of particular interest here are the reptile and fish bones that have been found here.
The Sparta Sand in particular is a thick bed that can be several hundred feet think. It is a fine to medium-grained sandstone that is typically light-colored, either a whitish or light gray, with thin beds or brown or grayish sandy clay and lignite. It has been considered an important aquifer for the region. The sediment is thought to have been laid down by rivers during a regression of the marine shoreline farther south. In other words, we are looking at the flood plain of a river meandering its way to the ocean, much like southern Arkansas and Louisiana is today. Only back then, the catfish grew much bigger than they do now.
So what do we know of this fish? We know it was a siluriform catfish, most likely in the Ictaluridae family, along with all the other North American catfish. It was probably something like the giant Mekong river catfish and lived in similar environments. The Eocene was warmer than it is now, so it was likely even more tropical than it is today. Beyond that, we don’t know a lot. The fossil has never been fully studied and described as far as I am aware. In 1983, Dr. John Lundberg, a noted expert in fossil catfish and currently chief curator at the Academy of Natural Sciences of Drexel University, corresponded with the AGS about studying it, but thus far, I don’t know what, if anything, came of it.
2017 is at an end. While the year has had a lot of things that will make us say good riddance, the year in paleontology was extraordinary. To give you an idea of just how extraordinary, let’s look at what has been discovered. Far too much has gone on, so we can’t look at everything, but if we just look at the new species that have been published, it will give us a decent proxy. Using that as a measure, what a year it has been.
111 angiosperms (flowering plants). One new species is Foveomonocolpites ravni, fossil pollen from the early Cretaceous of Isreal.
7 Gingoales, 20 conifers, 27 other seed plants. and 55 other plant fossils, and this doesn’t even include 4 new red algae, one of which is Rafatazmia chitrakootensis from India, the oldest known plant fossil at 1.6 billion years old.
23 cnidarians. including this jellyfish from the Cambrian.
68 bryozoans and 56 brachiopods,
82 malacostracans (crabs), 87 ostracods, and 9 other crustaceans
112 coleopterans, 2 dermapterans, 1 dictyopterans, 50 dipterans, 20 hemipterans, 47 hymenopterans, 5 mecopterans, 22 neuropterans, 25 odonates, 10 trichopterans, and 44 other insects
72 arachnids, 32 trilobites and 33 other arthropods
79 ammonoids and 31 other cephalopods, 140 gastropods, 71 bivalves, and 11 other molluscs
42 conodonts, 1 early jawless vertebrate, 5 placoderms, 22 sharks and their relatives, and 102 bony fish
3 temnospondyls, 3 lissamphibians, and 2 other amphibians
12 turtles, 9 crocodilians,
42 nonavian dinosaurs, including 9 ornithischians (including Zuul, the destroyer of shins and the most complete ankylosaur), 21 theropods, and 12 sauropods.
20 birds, 6 pterosaurs, 1 basal archosauriform named Teleocrater, and 3 other reptiles.
11 non-mammalian synapsids, 5 metatherians, 10 xenarthrans, 1 elephant, 4 sirens (dugongs and manatees), 5 bats, 25 ungulates, 14 cetaceans, 11 carnivorans, 6 lagomorphs (rabbits and hares), 66 rodents, 6 primates, 20 other eutherians, and 6 other mammals.
55 other animals, as well as 54 various other organisms, including foraminfera and others of uncertain affinities.
All told, 2003 new species. So whatever else happened this year, it was a good year for paleontology. Here’s hoping that 2018 is good all the way around.
If you are looking for a great place to begin your canoeing experience, or just a quiet river to float down with great views, you can’t go wrong with the Buffalo National River in Arkansas as it flows through the Ozark and Boston Mountains. In 1972, Congress declared the Buffalo to be a National River, the first river to be so designated in the Unites States, which protects it from industrial use and any construction that might change the natural character of the river. It is renowned for its clean water and spectacular bluffs. People come from all over to camp in the park, hike its trails, and float the river. Much of the river is easy to float, so a welcome adventure for novices, although the upper reaches can be challenging.
This is the first of many posts about the geology of the river and the fossils that can be found in the park. Please note that this is a national park, so collecting fossils within the park boundaries is strictly prohibited. However, many of the formations discussed herein can be found throughout large portions of the Ozarks, so if you want to collect fossils, consult a geologic map and find a road that runs through the formation outside the park to find suitable roadcuts. Fossil collecting is allowed on state land, so just make sure you are not in a national park, national forest, or on someone’s private land (unless you have their permission).
The Buffalo river cuts through several formations which are mostly Ordovician or Mississippian in age (~470 to 320 Mya). You can find geologic maps in pdf format of the Buffalo National River here and here.In the western reaches, the primary formation is the Everton Formation, but in the central and eastern portions of the river, the Boone Formation dominates. There are numerous bluffs displaying thick sections of the Boone.
The United States Geological Survey describes the Boone Formation as “mainly finely crystalline limestone with some cherty limestone and interbedded chert and minor shale. Approximately 400 ft. maximum thickness.” There is a lot of limestone in the Ozarks, but the nodules and thin beds of chert make the Boone stand out from the others.
It is early Mississippian in age, although exactly how old is a bit debateable. The USGS lists it as being in the Meramecian/Osagean stages, which places it mostly in the Middle Missippian. However, the Arkansas Geological Survey says it is in the Kinderhookian/Osagean stages, which are mostly early Mississippian. These stages are regional North American names, so you won’t find them on standard geological time scales meant to be used globally. At any rate, the Boone formed approximately 340-359 million years ago.
During the Paleozoic Era, the ocean had several cycles of raising and lowering sea levels. During the time the Boone Formation was forming, the region was a near shore marine environment, which explains the limestone and shale. The chert has typically been ascribed a biogenic origin, possibly the result of blooms of diatoms and radiolarians, both of which are single-celled organisms that make shells from silica, rather than the more common calcium carbonate which helped form the limestone. These organisms have also been presumed to form the Arkansas novaculite, a formation of metamorphosed microcrystalline quartz that reaches up to 900 feet in thickness. However, recent work indicates that both the Boone chert and the novaculite were formed from volcanic ash, created by an island-arc volcanic chain that existed about where the Ouachita Mountains are today.
Northern Arkansas is known for its widespread karst topography, meaning it has a lot of sinkholes and caves, most of which are in the Boone Formation. The cave systems are so extensive that at periods of very low flow, the entire Buffalo River is swallowed up and becomes subterranean in a few areas. The Boone forms the ceiling of the most famous cave in Arkansas, Blanchard Springs Caverns, which are well worth visiting if you find yourself in northwest Arkansas. On a side note, you may find references to the Boone in Blanchard Springs being as young as 310 million years old, but with better refinement of dating techniques and better dating of the rocks, that date has been pushed back.
The next posts in this series will cover the fossils that have been found in the Boone Formation. Stay tuned.
Today is National Fossil Day™. The National Park Service holds this annual event on the second Wednesday every year to coincide with Earth Science Week sponsored by the American Geosciences Institute. Earth Science Week highlights the important role of earth sciences in our everyday lives and “to encourage stewardship of the Earth.” National Fossil Day is, as NPS says, “held to highlight the scientific and educational value of paleontology and the importance of preserving fossils for future generations.”
In honor of the day, I am going to give you a whirlwind tour of some of our most outstanding fossils from all over the state. People may not think of Arkansas as being rich in fossils, but we have a rich natural history spanning 500 million years. To give you a quick summary of the wide array of fossils, just check out the map on the fossil page, reproduced below.
The most fossiliferous region in the state is the Ozarks, without a doubt. It is a favorite fossil collecting spot for many people, even though much of the area is national forest or national park owned, which prohibits fossil collecting. Nevertheless, fossils may be collected on any roadcut. I-65 near Leslie has several fossiliferous roadcuts. You are most likely to find abundant examples of crinoids, bryozoans like the screw-shaped Archimedes, clams and brachiopods, ammonoids (mostly goniatites), corals such as horn corals and tabulate corals, as well as the occasional echinoid and trilobite, along with many other types of fossils. This list of fossils makes it plain that the Ozarks are dominated by marine deposits, but you can find the occasional semi-terrestrial deposit loaded with plants like Calamites and Lepidodendron.
Top, left to right: Calamites, spiriferid brachiopod, blastoid echinoderm, goniatite ammonoid. Bottom left to right: Archimedes bryozoan, crinoid with calyx and fronds (very rare, mostly you just find pieces of the stalk).
There are a few fossils that particularly stand out. One is Rayonnoceras, a nautiloid ammonoid, which reached lengths of over two meters, making it one of the longest straight-shelled ammonoids ever found. The other is a shark named Ozarcus. While shark teeth are common, it is rare to find one that preserves parts of the skull and gill supports. At 325 million years, Ozarcus is the oldest one like this ever found and it changed the way we viewed shark evolution, indicating that modern sharks may be an offshoot of bony fish, not the other way around.
We can’t leave the Ozarks without talking about Conard Fissure, a spectacular collection of Pleistocene fossils. Barnum Brown excavated the first chamber of the cave in 1906, pulling out thousands of fossils or all kinds, many of which were new to science. Of course, of all of them, the ones that most people remember were 15 skeletons of Smilodon, the largest of the saber-toothed cats. The one pictured to the right is a cast of one from La Brea, California. All of ours are held at the American Museum of Natural History.
The Ouachita Mountains are not nearly as fossiliferous, but they have two important types of fossils that are commonly found: graptolites (below left) and conodonts (below right, not from AR, Scripto Geologica). Graptolites are thought to be closely related to pterobranchs, which are still living today, even though the graptolites themselves are all from the Paleozoic Era. Most of the time, Graptolites look like pencil marks on slate, but if you find a good one, you can see they are often like serrated files that may come branched or coiled. The reason these are important is because they are hemichordates, the closest group to the chordates, all animals with a spine (either a stiff rod or actual bone). Conodonts, on the other hand, are the closest we have to the earliest vertebrates, looking like nothing so much as a degenerate hagfish.
The coastal plain is quite fossiliferous and has attracted the majority of press because it is here where you will find Cretaceous aged rocks and that means dinosaurs and their compatriots. Here you will find thousands of Exogyra oysters. Scattered among them, you can find numerous shark teeth, along with teeth from Enchodus, the saber-toothed herring (although not really a herring), especially if you look in the chalk beds. You can also find the rare example of hesperornithids, extinct diving birds, as well as fossil crocodilians.
But of course, the main draws here are the marine reptiles and the dinosaurs. Mosasaur vertebrae are not uncommon, although the skulls are. More rarely, one can find plesiosaur (the article only mentions elasmosaurs, which are a type of plesiosaur, but most plesiosaur fossils in Arkansas cannot be identified that closely) vertebrae as well.And then of course are the dinosaurs. We only have a few bones of one, named Arkansaurus, but we have found thousands of footprints of sauropods, the giant long-necked dinosaurs. Since the sauropods that have been found in Texas and Oklahoma are titanosaurs, such as Sauroposeidon, it is a good bet the footprints were made by titanosaurs. A few tracks have also been found of Acrocanthosaurus, a carnivorous dinosaur like looked something like a ridge-backed T. rex. Acrocanthosaurus reached almost 12 meters, so while T. rex was bigger, it wasn’t bigger by much.
Top left: Mosasaur in UT Austin museum. Top right: Plesiosaur vertebra from southern AR. Middle left: reconstruction of Arkansaurus foot. Middle right: statue of Arkansaurus (out of date). Bottom left: Sauropod footprints. Bottom right: Acrocanthosaurus footprint, Earth Times.
The eastern half of the state is dominated by river deposits from the Mississippi River, so the fossils found there are mainly Pleistocene aged, with the exception of a few earlier Paleogene fossils near Crowley’s Ridge. Pleistocene deposits can be found all over the state, as they are the youngest, but are most common in the east. In these deposits, a number of large fossils have been found. A mammoth was found near Hazen, but we have almost two dozen mastodons scattered over the state. I already mentioned Smilodon, but we also have , the giant short-faced bear, dire wolves, giant ground sloths, and even a giant sea snake named Pterosphenus. Most unusual of all is a specimen of Basilosaurus, which despite its name meaning king lizard, was actually one of the first whales. Considering the month, I would be remiss not to include Bootherium, also known as Harlan,s musk ox, or the helmeted musk ox.
Top left: Mastodon on display at Mid-America Museum. Top right: Basilosaurus by Karen Carr. Bottom left: Arctodus simus, Labrea tar pits. Wikipedia. Bottom right: Bootherium, Ohio Historical Society.
This is nowhere near all the fossils that can be found in Arkansas, but it does give a taste of our extensive natural history covering half a billion years. After all, we wouldn’t be the Natural State without a robust natural history. Happy National Fossil Day!
Monday I posted a set of pictures showing an Arkansas fossil. Were you able to figure it out. Check below for the answer.
This skull and mandible comes from the Madrean Archipelago Biodiversity Assessment (MABA) website. I couldn’t find a good picture of an actual fossil, so I used this modern example instead. Below is a living version.
The skull is that of Myotis leibii, the eastern small-footed Myotis. Myotis bats are also called mouse-eared bats, the most famous of which is the little brown bat, Myotis lucifugus. The other fossil bat in Arkansas is the big brown bat, which is not in the genus Myotis at all. It is in the genus Eptesicus (E. fuscus specifically).
I have talked about E. fuscus before, where I talked a bit about bats in general. I didn’t go into their phylogeny at all, so I will talk about that here. Bats as a whole belong to the order Chiroptera, which is the sister group to a group called Fereuungulata. That group includes artiodactyls, cetaceans (whales and dolphins), carnivorans, and pangolins. Altogether, Chiroptera and Fereuungulata form the horribly named Scrotifera. Why do I say it is horribly named? Besides the fact that naming such a large group after scrotums is a bit odd, take a look at the simplified mammal phylogeny illustrated by Darren Naish.
Notice what is NOT in Scrotifera. That’s right. Primates, such as us. Yes, we are more closely related to rats and squirrels than we are to bats, dolphins, or cats and dogs. We are also not included in the group named for a feature we possess.
Both Myotis and Eptesicus are Vesper bats, meaning they belong in the family Vespertilionidae, along with over 300 other bat species. When it comes to diversity, mammals could easily be described as rodents, bats and their less common relatives, seeing as how those two groups include 60% of all mammals. Vesper bats are in the suborder Microchiroptera, the micro bats. The other suborder, Megachiroptera, is composed of the fruit bats like the flying foxes. The two suborders are rather lopsided in numbers, with just under 200 species in Megachiroptera and over 1000 in the Microchiroptera. This is the traditional classification at any rate.
There is another phylogeny that splits it up slightly differently and gives them different names. Megachiroptera has become Yinpterochiroptera and includes the horseshoe bats in the group called Rhinolophoidea as well as the lesser and greater false vampire bats in the genus Megaderma. Everything else that was in Microchiroptera is in Yangochiroptera.
So returning to the vesper bats, these include most of the bats people are likely to run into, which is why the bats in this group are sometimes called common bats. Most of the bats in this group have rather plain faces and are insectivores. Myotis leibii itself belongs in the group Myotinae, marked in the red box in the phylogeny below, which was also put together by Darren Naish.
The interesting thing about this is that Eptesicus, the big brown bat, is in the serotine clade, up near the top of the tree and quite a distance away from Myotis, the little brown bat. Eptesicus is also sometimes called a house bat, but the house bats are in the group Scotophini, which while still in Vespertilioninae, is not closely related within the group. This is part of the reason common names can get confusing. just because the common names are similar and overlap doesn’t necessarily mean they are at all closely related.
M. leibii itself lives in forests throughout eastern North America, in spotty patches from Canada to Arkansas and Georgia. It is a small bat, weighing only about 5 grams and with a wingspan of less than 10 cm. Unusually for its size, it is long lived, living as long as 12 years and tolerates the cold better than most other bats, so spends less time in hibernation than other bats.
The fossil record of M. leibii is sparse, although the fossil record for Myotis in general is fairly good for bats. According to molecular data, the genus Myotis first appeared roughly 16 Mya, with the North American clade splitting off no more than 9 Mya. However, the actual fossil data indicates Myotis is far older, with the earliest known Myotis fossil being 33 Mya to the earliest Oligocene, although in North America, the record only extends to the late Miocene no more than 23 Mya. Interestingly, the fossil record for M leibii demonstrates a range far greater than the current distribution, with fossils being found as far as Oregon. In Arkansas, fossils are limited to one spot, which happens to be the same spot Eptesicus has been found: pleistocene deposits within the Conard fissure. If one looks in the original publication of Conard Fissure by Barnum Brown, one will find Vespertilio fuscus and Myotis subulatus, but both of those names have been changed in the intervening 110 years, to Eptesicus fuscus and Myotis leibii.
It is long past time I resurrected Monday Mystery fossils. So to celebrate the season, here is a little animal whose relatives, or at least representations thereof, shall be widely seen over the next month.
If you think you know what this is, please leave your identification in the comments. I will let everyone know what it is and where fossils like this have been found in Arkansas on Friday. Have a great October!